Symbiotic efficiency of cowpea Bradyrhizobium strains in Cerrado soils

Abstract

The obejctive of this study was to evaluate the phylogenetic relationships of Bradyrhizobium strains, and the contribution of these strains to cowpea biological nitrogen fixation in Cerrado soils. To elucidate the phylogenetic relationships among strains, their 16S rDNA gene was extracted, amplified and sequenced. In order to evaluate the symbiotic efficiency, total N, plant dry matter, nodular mass and acetylene reduction in a greenhouse experiment, and nodular occupation, in a field experiment, were determined. Most part of the strains belonge to B. elkanii, and at least ten of the analyzed strains, independently of the species, presented high capacity to fix N₂. The strains BR3262, BR3280 (characterized as B. elkanii), BR3267, BR3287 and BR3288 (Bradyrhizobium sp.) exhibit a potential as inoculant for cowpea, due to their high biological nitrogen fixation.